DNA replication Flashcards
Why is DNA replication considered semiconservative?
because when the cell replicates, each cell will contain one strand of DNA from the original cell, while the second strand of DNA will be a new, replicated strand
In which direction does DNA replication occur?
5’ to 3’ direction
What is the origin of replication?
- the sequence that signals where replication should start
- prokaryotes have one origin of replication, while eukaryotes have multiple
What is the enzyme that comes to the origin of replication and starts unwinding the DNA?
helicase
What is the enzyme that prevents the closure of the DNA molecule once it is unwound by helicase?
single stranded binding proteins (SSBP’s)
Which enzyme prevents supercoiling downstream as the helicase is unwinding the DNA?
topoisomerase-it cuts and relaxes the DNA to prevent supercoiling
Which enzyme starts at the origin of replication sequence and lays the RNA primer in the 5’ to 3’ direction?
primases
Which enzymes is able to bind to the RNA primer and start synthesizing DNA?
DNA polymerase
-it also proofreads and removes RNA primer
What is DNA polymerase?
the enzyme that binds to the RNA primer and starts synthesizing DNA. It also has ability to proofread and remove the RNA primer
What is helicase
unwinds DNA so it can be replicated
What is the leading strand?
refers to the strand that is synthesized continuously into the widening of the replication fork
What is the lagging strand?
refers to the strand that is not synthesized continuously because it must wait for the replication fork to widen before beginning to polymerize
What are Okazaki fragments
The lagging strand fragments that contain both RNA and DNA
What enzyme linkes Okazaki fragments together after the RNA primer is removed?
DNA ligase
What is theta replication?
refers to prokaryotic DNA replication; as the circular DNA is replicated, one original chromosome strand falls off from the other (which creates an image that looks like the greek letter theta)
What are the 2 prominent DNA polymerases involved in prokaryotic DNA replication?
DNA Polymerase I & DNA Polymerase III
In prokaryotes, what are the functions of DNA Polymerase III?
- this is the main replicating enzyme; it synthesizes DNA with high processivity and accuracy (is a fast 5’ to 3’ polymerase)
- it takes over for DNA Pol 1 ~400bp downstream from the ORI sequence.
- is a 3’ to 5’ exonuclease (the proofreading ability; is able to read the last base it filled in to ensure it is correct. If the last base filled in is not correct, it will replace it with the correct base)
- has no known function in DNA repair
In prokaryotes, what are the functions of DNA Polymerase I?
- This starts adding nucleotides at the RNA primer (5’ to 3’ polymerase); also has 5’ to 3’ exonuclease activity so it can remove the RNA primer and replace it with DNA in 5’ to 3’ activity.
- This is the “backup” for DNA Polymerase III; has low processivity and therefore is a slow 5’ to 3’ polymerase
- is a 3’ to 5’ exonuclease (the proofreading ability; is able to read the last base it filled in to ensure it is correct. If the last base filled in is not correct, it will replace it with the correct base)
- functions in DNA excision repair
In prokaryotes, what are the functions of DNA Polymerase II?
- 5’ to 3’ polymerase (functions as a DNA Polymerase III backup)
- 3’ to 5’ exonuclease
- has a function in DNA repair pathways
In prokaryotes, what are the functions of DNA Polymerase IV & V?
- main function is in DNA repair: play an important part of the prokaryotic checkpoint pathway, as they function to stall other polymerase enzymes at replication forks when the DNA repair pathway has been activated
- these are error prone in 5’ to 3’ polymerase activity
In eukaryotes, DNA polymerases are complex ______ enzymes
multisubunit
Eukaryotic DNA polymerases has a subunit that works as a ______, and also a subunit that works as a ______
polymerase, primase
When helicase unwinds the DNA for replication, the open strands are referred to as an ____complex
open
What is the role of primase in DNA replication?
an RNA polymerase that lays down the RNA primer on the template strand
